This invention relates to a method and composition for cleaning surfaces such as the exterior brick and stone walls of buildings coated with grime by airborne gaseous and solid pollutants common in industrialized centres.
It is known to clean masonry surfaces by sand blasting and by high pressure water jets. However, the former is expensive, creates pollution, damages the texture of the surface to be cleaned and may damage glass window panes, while the latter often is not effective in removing many years' accumulation of deposits. Aqueous solutions of alkaline and acid substances are known, as typified in U.S. Pat. Nos. 2,837,484; 3,523,825; 3,681,141 and 3,379,645, but known solutions generally have not been effective in removing surface deposits, have been excessively corrosive of the underlying brick or stone, or have been hazardous to use.